The present invention relates to the field of measurement devices, and, more specifically, to measuring devices that are capable of determining or actively sensing the edge position of an object with respect to a selected field of view.
Determining the position of an object is a common requirement in various industries, for example, to monitor products during the fabrication process. Many products today, although mass produced, are intricately designed, thus requiring precise cutting and machining of the product during the various stages of production. Moreover, increasing automation of modern manufacturing plants demands instrumentation and control systems that are able to determine the position of the product at the various stages of production in a fast and accurate manner.
Prior art edge position measuring devices include position detectors which illuminate an object as it passes, and detect scattered light using a linear diode array. The prior art also includes obstruction detectors which use a scanning laser in conjunction with a retroreflective surface and, an optical detector, and includes imaging systems that apply an image onto a multi-element ccd sensor. However, the foregoing devices usually require associated circuitry that is relatively complex. Accordingly, such edge position measuring devices are costly. Moreover, such devices are often incapable of generating sufficient gray-scale contrast between the edge of the object being monitored and the background, or because they are characterized by an inherently low signal to noise ratio, ultimately affecting the system's ability to accurately determine the position of the object being monitored.
In one prior art form, a so-called reflex proximity sensor uses a light emitting source which directs a beam toward a retroreflective surface, which reflects incident light back towards the source. A collimating lens is positioned in the beam path to produce a collimated beam of light. The portion of the beam which reflects off the retroreflective surface passes back through the collimating lens, and generally irradiates a circular region on a photodetector. A beamsplitter is used to direct the return beam to the detector. The position and size of the optical components are selected so that a desired spot size is established at the detector. As the object being monitored traverses the beam, between the collimating lens and the retroreflective surface, the leading (or trailing) edge establishes a change in intensity level of the beam portion that reaches the detector. The output of the detector provides a signal representative of the passage of the leading (or trailing) edge. However, even these systems provide less than desired performances. Particularly, the circular cross-section of the beam often provides unacceptable resolution limits and sensitivity along the detection axis.
As the above-described and other prior art position measuring devices have proven less than optimal, an object of this invention is to provide an improved edge position measuring system.
Another object of the invention is to provide an edge position measuring system that evinces a fast system response time.
Still another object of the invention is to produce a relatively low cost apparatus that employs simple system electronics.
Yet another object of the invention is to provide a position measuring device which may be readily integrated with pre-existing assembly line equipment.
Other general and more specific objects of this invention will in part be obvious and evident from the drawings and description which follow.